The present invention relates generally to the propulsion of objects in three-dimensional space, and more particularly to the self-directed propulsion of such objects.
Since the dawn of civilization, commerce and warfare have depended critically on the travel of man and his material by land and water, and, more recently, through air and space. The evolution of manmade craft has partly reflected man""s observation of swimming and flying creatures, as well as constraints he has imposed for his creature comfort. The wide variety of resulting successful designs share a common aspect; their steering or control systems are designed, in large part, to suppress angular motion such that the craft maintains an upright pose and travel is straight and level, except during the occasional turn or change in altitude. This suppression of angular motion to preserve an upright pose is frequently called xe2x80x9cattitude controlxe2x80x9d. Overturning or capsizing is usually perceived as disastrous.
Travel on land or on the surface of water is two-dimensional (2D), and simple steering devices keep travel straight while gravity and the ground reaction force or buoyancy maintain attitude control. Devices that travel in three-dimensional (3D) space, such as planes and submarines, generally require complex control systems for attitude control such that travel is straight and level. The requisite control systems and actuators (e.g. ailerons, wing flaps, trim tabs, counter-rotating propellers) typically arc expensive, complex, mission-critical, subject to failure, and not readily scaleable to suit other desirable applications, such as inexpensive and robust, small, self-steering munitions. The motion and orientation of any device in three dimensional space requires the simultaneous control of six degrees of freedomxe2x80x94three degrees of freedom in translation and three degrees of freedom in rotation. Thus the translational velocity (V) and the rotational velocity (xcfx89) completely describe the 3D motion of any device.
In the absence of control, almost every device has a non-zero rotational velocity. For example, a person walking in a blinding snowstorm turns imperceptibly to one side, and subsequently walks in circles. For 3D motion, the default trajectory is a helix (see FIG. 1a). The magnitudes of V and xcfx89, and the angle formed by these vectors, determine the axis (K), radius (r), pitch (p), and pitch angle (xcex8). To a first approximation, K is parallel to xcfx89, and the angle formed by V and xcfx89 equals the pitch angle (xcex8) of the helical trajectory. For example, if xcfx89 is perpendicular to V then the resulting trajectory is a circle (pitch is zero and pitch angle is 90xc2x0xe2x80x94FIG. 1b). If xcfx89 is parallel to V then the resulting trajectory is straight-line motion with rotation of the device about the direction of motion (radius is zero and pitch angle is 0xc2x0xe2x80x94FIG. 1c). For all other angles xcex8 between V and xcfx89 (0xc2x0 less than xcex8 less than 90xc2x0), pitch and radius are non-zero (FIG. 1a).
Importantly, the axis of the helix defines the net direction of motion. Because the axis is parallel to xcfx89, orientation of a helical trajectory requires that xcfx89, not V, be pointed in the desired direction.
Prior art solutions simplify orientation by imposing two restraints on the device""s motion. The first of these restraints (identified as Restraint 1) is that one side of the device (designated the xe2x80x9cnosexe2x80x9d) travels forward, i.e. the translational velocity V is largely restrained to one degree of freedom with respect to the body of the device. Thus, airplanes, missiles, and torpedoes all travel with their noses extending forward. Restraint 1 arises for two reasons: (a) most devices are built to go from point-to-point and, subsequently, (b) most man-made devices have thrusters that point in only one direction; e.g., the jets of a plane thrust rearward, in a direction parallel to the fuselage, and the propeller of a torpedo thrusts rearward in a direction parallel to the hull.
The second of these restraints (identified as Restraint 2) uses attitude control (described above) in which the orientation of the device is almost always restrained with respect to gravityxe2x80x94typically one side of the device (designated the xe2x80x9ctopxe2x80x9d) faces up with respect to gravity. Restraint 2 is required for vessels carrying people, but it is a restraint that is almost always applied to man-made devices that do not carry people, such as unmanned airplanes and unmanned submersibles. For such devices, rotation along the three degrees of rotational freedom have specific names: xe2x80x9cyawxe2x80x9d for rotation about the top/bottom axis (the axis that is usually parallel to gravity); xe2x80x9crollxe2x80x9d for rotation about the fore/aft axis (the axis parallel to the direction of motion); and xe2x80x9cpitchxe2x80x9d for rotation about the third orthogonal axis (the left/right axis). (Note that the xe2x80x9cpitchxe2x80x9d of a helix, p, should not be confused with the xe2x80x9cpitchxe2x80x9d component of rotation.)
Steering of devices using Restraints 1 and 2 is accomplished by turning, or rotating, the device to make the translational velocity V point in the desired direction of motion. For example, if a northbound device turns east, then the device must yaw, turning to starboard. The most common example is steering an airplanexe2x80x94yaw, pitch, and roll are permitted only during turns and only over narrow limits in normal use. After a turn the plane always returns to its original orientation with respect to gravityxe2x80x94with the top up and the nose forward. In between turns, the rotational velocity xcfx89 of the device is usually small; in fact, the attitude control system of the device usually strives to keep xcfx89 at or near zero to maintain orientation with respect to gravity. These are control strategies arising from the navigation of boats on the surface of water; nevertheless, other devices, like submarines and torpedoes, use similar control strategies.
Unfortunately, attitude control during periods of straight-line motion and precise control of the rotational velocity during turns require extensive and usually complex control mechanisms, including multiple sensors, actuators, control surfaces, and control circuits. Thus, control of a device in three dimensions is one of the most demanding and costly factors in design and manufacture. As such, a controllable device that lacks these complex control mechanisms would be desirable.
In view of the foregoing, it is an object of the present invention to provide a device capable of navigating in three dimensional space that operates under different restraints than Restraints 1 and 2 above.
It is also an object of the present invention to provide such a device that is self-guided.
It is an additional object of the present invention to provide such a device that lacks the complex control mechanisms of prior art devices.
These and other objects are satisfied by the present invention, which is directed to self-orienting devices and associated methods for using the same that exploit the default helical trajectory of otherwise uncontrolled devices rather than suppressing it. A self-orienting device of the present invention comprises: a housing; a sensor mounted to the housing that is sensitive to a signal field and configured to produce a signal responsive to the signal field; a translation-inducing unit associated with the housing; a rotation-inducing unit associated with the housing, wherein the translation-inducing unit and the rotation-inducing unit are configured such that the housing travels along a helical trajectory; and a controller operably associated with the sensor for controlling the output of either or both the translation-inducing unit and the rotation-inducing unit, wherein the controller is configured such that it receives the signal from the sensor and, responsive to the signal, controls the output of either or both the translation-inducing unit and the rotation-inducing unit.
Devices of the present invention travel along a helical trajectory, continuously rotating as they travel, and can self-orient in 3D by pointing the rotational velocity xcfx89 in the desired direction. Pointing xcfx89 is accomplished by making the components of xcfx89 (similar to roll, pitch, and yaw) functions of the signal to which the device is orienting, as explained later. Simple functions work well; in fact, if xcfx89 changes as almost any function of signal intensity, then orientation to the signal is the only stable outcome. Such devices have no need for the complex control systems required for attitude control, permitting orientation in 3D with relatively simple, robust, and inexpensive control systems.
In fact, self-orientation in 3D space can be accomplished using devices having only a single channel of information (one sensor, one actuator) when responding to a signal field. Exemplary signal fields include light, magnetic fields, and gradients of temperature, chemical concentration, and depth. Such devices can be employed to perform such tasks as locating lost objects, identifying foreign objects, performing transect sampling, guiding munitions, disabling mines, delivering chemical agents, and the like.